1. Field of the Invention
The present invention relates to an ink jet recording system used for copying machines, facsimile machines, word processors, printers as an output terminals for work stations, personal computer, a host computers or optical disc apparatuses, video output printers, handy or portable printers to be coupled to the above-described equipment or the like and more particularly to a substrate for a recording head where an electrothermal converting element which generates a thermal energy used for recording information and functional elements for recording are configured on the common substrate plate, a recording head having the substrate, an ink jet recording system having the recording head and a method of manufacturing the substrate.
2. Related Background Art
Conventionally, recording heads generally have the following structures. Electrothermal converting elements are arranged in an array geometry and formed on a single crystal silicon substrate plate. A driver circuit for driving the electrothermal converting elements is formed outside the silicon substrate plate by arranging functional elements such as transistor arrays and/or diode arrays. Electric connections between the electrothermal converting elements and the functional elements such as transistors arrays are made by flexible cables, wire bonding or the like.
On the other hand, for the purpose of simplification of a structure of the above-mentioned recording head, reduction of the defective components during manufacturing processes, and improvements of uniformity of characteristics of electronic devices and reproducibility of the device, an ink jet recording head was developed having electrothermal converting elements and functional elements, both of which are formed on the common semiconductor substrate plate, such as disclosed in Japanese Patent Application Laying-open No. 72867/1982.
FIG. 1 shows a part of a recording head formed on a common semiconductor substrate including an N type epitaxial layer plate. Reference numeral 901 denotes a semiconductor substrate plate formed by a single crystal silicon. Reference numeral 902 denotes an N type semiconductor collector region formed by epitaxial growth. Reference numeral 903 denotes an ohmic contact region of N type semiconductor containing a high impurity concentration. Reference numeral 904 denotes a base region of P type semiconductor. reference numeral 905 denotes an emitter region of N type semiconductor containing a high impurity concentration. The regions 902 to 905 define a bipolar transistor 920. Reference numeral 906 denotes a silicon oxide layer as heat accumulating and insulating layer. Reference numeral 907 denotes a hafnium boride layer as a heat generating resistance layer. Reference numeral 908 denotes an aluminium electrode. Reference numeral 909 denotes a silicon oxide layer as a protective layer. The regions 901 to 909 form a substrate 930 for a recording head. In the layer configuration shown in FIG. 1, reference numeral 940 denotes a heating portion. A top plate 910 defines a liquid passage (ink passage) 950 in cooperation with the substrate 930.
Various improvements and proposals have been made with respect to the recording head having structures mentioned above. Recently, specific performance improvements have been further required in the recording head, such as attaining higher speed driveability, saving energy consumption, higher integration density, lower cost, higher reliability and high level functionality.
When using the above-mentioned substrate as a part of an ink jet recording head, or of a thermal head, effective steps must be taken to prevent the head or the entire recording apparatus from increasing its size and cost. Here, the ink jet recording head is composed of, for example, discharging orifices for discharging recording liquid (ink), liquid passages communicating to the orifices, electrothermal converting elements which are provided corresponding to orifice and function as discharge energy generating elements; and the thermal head is used for thermal recording.
Commerical success cannot be expected without supplying high quality recording heads at low cost, which is achieved by constructing low cost recording heads by implementing high-density integration of functional elements and reduction of the area of a chip as substrates of the recording heads. For this, functional elements such as diodes, transistors or the like must be made smaller.
With the ink jet recording head, however, an electric current of about 200-400 mA is needed to effectively drive electrothermal converting elements disposed in the head. This presents the following problems involved in the reduction of sizes of diodes or the like.
(1) The electric current is concentrated on a portion of a diode. This will sharply increase the current density of the portion, thereby damaging a junction of the diode.
(2) A high voltage is required to ensure a sufficient electric current for driving the head. This necessitates the change of the arrangement of the entire system.
(3) A current density of the junction will be saturated when it exceeds a certain value, which prevents the sufficient current.
In particular, the inventors have found through a number of experiments that the construction of recording heads used by ink jet recording apparatuses must be determined taking sufficient account of the effect of heat which is produced by semiconductor devices, electrothermal converting elements, or the like, because a liquid (ink) is used in the recording heads.